The main objective of the proposed research is to characterize the earliest differentiative cellular events in the embryonic central nervous system in order to obtain insight into possible mechanisms of normal and abnormal brain development. Recent advances in biomedical technology provide an unparallelled opportunity to examine cell-to-cell interactions at developmental stages that were until recently not accessable to analysis. The expression of specific brain cell phenotypes will be examined by immunocytochemical methodology using monoclonal antibodies, which allows the tracing of the onset of cell differentiation prior to any visible sign of morphological maturation. Specifically, I will attempt to determine the existence of specific cell lines within the embryonic proliferative zones prior to cell migration. Two model systems will be utilized: (1) pyramidal and granule cells of the mouse hippocampal formation will be separated using Percoll density gradient centrifugation and enriched fractions will be used for immunization to obtain monoclonal antibodies to these neural cell types, (2) monoamine neurotransmitter molecules will be linked to proteins and used to obtain high titer monoclonal antibodies capable of detecting minute quantities of the neurotransmitters in morphologically immature cells of the brainstem. Cell class-specific and transmitter-specific antibodies may enable detection of cell precursors in the proliferative or migratory zones, thus providing new insights into the relationship of early cell determination to subsequent differentiative events. The early establishment of cell lines in the proliferative zones may be essential for subsequent expression of proper phenotypes that lead to the normal organization of complex neural networks, while the failure of timely cell differentiation may lead to a chain of abnormal interactions resulting in a malformed brain.